Composite Core and Method of Making Same

ABSTRACT

A composite core includes a plurality of tubes, each the plurality of tubes comprising a plurality of fibers disposed in a polymeric matrix. Adjacent tubes of the plurality of tubes are adhesively bonded to one another along sides of the adjacent tubes. A method of making a composite core includes the steps of providing a plurality of tubes, each of the plurality of tubes including a plurality of fibers disposed in a polymeric matrix, and adhesively bonding adjacent tubes of the plurality of tubes along sides of the adjacent tubes. A method of making a composite core such that a removable band is included in the core, the removable band being configured to be removable through a procedure subsequent to the cure of the composite core, thereby producing gaps in the core.

BACKGROUND 1. Field of the Invention

The present application relates in general to the field of compositestructures.

2. Description of Related Art

Composite structures, such as composite sandwich structures, are oftenused because of their high strength-to-weight ratio. Such structures arefrequently used in the manufacture of aircraft, such as airplanes,helicopters, and the like. Composite sandwich structures typicallyinclude an upper skin, a lower skin, and a core adhesively bondedbetween the upper skin and the lower skin. The upper and lower skins aremade of a composite material, such as carbon, graphite, glass fibers, orthe like disposed in a polymeric matrix, such as epoxy,polyetheretherketone, or the like. The core often comprises a honeycombstructure made from resin-infused paper.

The use of conventional sandwich structures, however, is limited in someapplications because the core of the sandwich structure fails to providesubstantive mechanical strength in some implementations. In other words,the strength of such a conventional sandwich structure is limited by thestrength of the core.

Efforts have been made to manufacture core that provides better specificmechanical strength at a reduced cost. One particular honeycomb coreutilizes a plurality of composite webs or ribbons extending across thecore, such that each of the webs defines one-half of a row of cells ofthe core. Such an approach doubles the wall thickness of adjacent cellnodes effectively increasing the weight of the core by approximately 30%without a comparable increase in load carrying capability. One drawbackwith a stacked ribbon block is the doubling of some walls where theribbons contact each other resulting in different stiffness and strengthin the ribbon direction and in the perpendicular direction to theribbons. The core is also difficult to tailor in the ribbon direction.In addition, if a load concentration exists in the core, it is difficultto manufacture a core block that has thicker cell walls only in theregion local to the concentration. Furthermore, there is a potentialweakness in the joint where the ribbons intersect, especially in coreblock comprising a plurality of procured ribbons bonded in a secondaryoperation. If an unbalanced or unsymmetrical layup is used in eachribbon, the ribbon will distort or twist after cure, thereby making astacking procedure of a block of ribbons more difficult and alsotrapping residual stresses.

There are many cores well known in the art for use in composite sandwichstructures; however, considerable room for improvement remains.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the embodiments of thepresent application are set forth in the appended claims. However, theembodiments themselves, as well as a preferred mode of use, and furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a perspective view of an illustrative embodiment of acomposite core according to the present application;

FIG. 2 is an enlarged, cross-sectional view of a portion of thecomposite core of FIG. 1 taken along the line 2-2 of FIG. 1;

FIGS. 3-8B are stylized, top, plan views of illustrative fiberconfigurations of a portion of the core of FIG. 1;

FIGS. 8C and 9 are enlarged, cross-sectional views of certainembodiments of a portion of the core of FIG. 1, as indicated in FIG. 2;

FIG. 10 is a cross-sectional view of an illustrative embodiment,alternative to that of FIG. 2, of a composite core according to thepresent application;

FIG. 11 is a stylized, side, elevational view of a sleeve of the presentapplication being braided, illustrating one particular embodiment of amethod according to the present application for making the sleeve;

FIG. 12 is a stylized, side, elevational view of the sleeve of FIG. 11being placed on a mandrel, further illustrating the method of FIG. 11 ofmaking the sleeve;

FIG. 13 is a stylized, side, elevational view of a sleeve of the presentapplication being braided onto a mandrel, illustrating one particularembodiment of a method, according to the present application, for makingthe sleeve;

FIG. 14 is a stylized, top, plan view of an illustrative embodiment of acomposite core tube of the present application being made using afilament winding process, illustrating one particular method, accordingto the present application, for making the composite core tube;

FIG. 15 is a stylized, top, plan view of an illustrative embodiment of acomposite core tube of the present application being made using a fiberplacement process, illustrating one particular embodiment of a method,of the present application, for making the composite core tube;

FIG. 16 is a stylized, perspective view of an alternate method,according to the present application, for making a composite core tubeof the present application;

FIG. 17 is a stylized, exploded, cross-sectional view of a plurality ofmandrels and composite core tubes as assembled for processing theplurality of composite core tubes into a composite core of the presentapplication;

FIG. 18 is a stylized, cross-sectional view illustrating one particularembodiment of a method for processing a plurality of composite coretubes into a composite core of the present application;

FIG. 19 is a stylized, exploded, cross-sectional view of a plurality ofexpandable mandrels and composite core tubes as assembled for processingthe plurality of composite core tubes into a composite core of thepresent application;

FIG. 20 is a stylized, cross-sectional view illustrating one particularembodiment of a method for processing a plurality of composite coretubes in expandable mandrels, into a composite core of the presentapplication;

FIG. 21 is a stylized, side, elevational view of an illustrativeembodiment of a composite sandwich structure according to the presentapplication;

FIG. 22 is a stylized, top, plan view of the composite sandwichstructure of FIG. 21;

FIG. 23 is a cross-sectional view of the composite sandwich structure ofFIG. 21, taken along the line 23-23 in FIG. 22; and

FIGS. 24 is a stylized, top, plan view of illustrative fiberconfiguration of a portion of the core of FIG. 1.

While the system and method of the present application are susceptibleto various modifications and alternative forms, specific embodimentsthereof have been shown by way of example in the drawings and are hereindescribed in detail. It should be understood, however, that thedescription herein of specific embodiments is not intended to limit theinvention to the particular embodiment disclosed, but on the contrary,the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the process of thepresent application as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the application are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present application, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

There is a need for an improved core for use in composite sandwichstructures.

Therefore, it is an object of the present application to provide animproved core for use in composite sandwich structures.

This and other objects are achieved by a composite core, which includesa plurality of tubes, each of the plurality of tubes comprising a singletow or split tow of fibers wound in a single candy stripe pattern.Adjacent tubes of the plurality of tubes are placed adjacent to oneanother along sides of the adjacent tubes. A resin is introduced intothe preform by a number of means, including vacuum assisted resintransfer molding, resin film infusion, or towpreg.

Another object of the present application allows for the winding angleto be varied in order to provide for the optimum core shear andcompression strength. The winding angle can be spaced apart to reducethe amount of material used and provide for a porous core wall with aplurality of small holes.

This and other objects are achieved by a composite core, which includesa plurality of tubes, each the plurality of tubes comprising a pluralityof fibers disposed in a polymeric matrix. Adjacent tubes of theplurality of tubes are adhesively bonded, or infused, to one anotheralong sides of the adjacent tubes.

In another aspect of the present application, a method of making acomposite core is provided. The method includes the steps of providing aplurality of tubes, each of the plurality of tubes including a pluralityof fibers disposed in a polymeric matrix, or subsequently infusing witha polymeric matrix, and adhesively bonding adjacent tubes of theplurality of tubes along sides of the adjacent tubes.

In yet another aspect of the present application, a composite sandwichstructure is provided. The composite sandwich structure includes a firstskin, a core, and a first adhesive layer adhesively bonded, infused, orotherwise attached to the first skin and a first face of the core. Thecore includes a plurality of tubes, each the plurality of tubescomprising a plurality of fibers disposed in a polymeric matrix, suchthat adjacent tubes of the plurality of tubes are adhesively bonded, orotherwise attached to one another along sides of the adjacent tubes.

The present application represents a composite, open-celled core and amethod of making the composite core. The core includes a plurality oftubes (i.e., hollow, cylindrical structures) arranged in atwo-dimensional array, such that adjacent tubes are adhesively bonded toone another. Each of the tubes comprises a plurality of reinforcingfibers disposed in a polymeric matrix. In one embodiment, at least oneof the tubes comprises a plurality of braided fibers disposed in thepolymeric matrix. In another embodiment, at least one of the tubescomprises a plurality of fibers formed generally in a helical shapedisposed in a polymeric matrix. The tubes may take on many differentcross-sectional configurations, such as triangular, square, rectangular,pentagonal, hexagonal, heptagonal, octagonal, or the like. Furthermore,the core may include a combination of tube shapes. For example, the coremay include a combination of octagon shaped tubes and square shapedtubes in a geometric pattern.

FIG. 1 depicts a first illustrative embodiment of a composite,open-celled core 101 according to the present application. Core 101comprises a plurality of tubes 103 arranged in a two-dimensional array.Note that only two tubes 103 are labeled in.

FIG. 1 for clarity. Each of tubes 103 defines a passageway or “cell” 105extending therethrough. Core 101 may comprise any suitable number, size,cross-sectional shape, and construction of tubes 103, as will bediscussed in greater detail below.

FIG. 2 depicts a cross-sectional view of a portion of core 101 takenalong a line 2-2 in FIG. 1. Each of tubes 103 comprises a plurality ofreinforcement fibers disposed in a polymeric matrix. For example, tubes103 may comprise fibers comprising one or more of carbon, graphite,glass, an aromatic polyamide (i.e., “aramid”) material, a variant of anaromatic polyamide material (e.g., a polyparaphenylene terephthalamidematerial, such as Kevlar® by E. I. du Pont de Nemours and Company ofRichmond, Virginia), or the like. The scope of the present application,however, encompasses fibers comprising any suitable material orcombination of materials. The polymeric matrix may comprise any suitablethermoplastic or thermosetting resin. Exemplary resins include epoxy,polyimide, polyamide, bismaleimide, polyester, vinyl ester, phenolic,polyetheretherketone (PEEK), polyetherketone (PEK), polyphenylenesulfide (PPS), and the like.

The fibers of tubes 103 may be oriented in one or more directions andmay be woven or unwoven. Exemplary embodiments of fiber arrangements oftubes 103 are shown in FIGS. 3-8B. FIG. 3 depicts one illustrativeembodiment of a portion of tube 103 indicated in FIG. 1. In theillustrated embodiment, tube 103 comprises a plurality of fibers 301(only one labeled for clarity) extending in a first direction and aplurality of fibers 303 (only one labeled for clarity) extending in asecond direction. It should be appreciated that tube 103 mayalternatively only include fibers 301 arranged in a single direction,such as a uniaxial or helical fiber configurations. It should be notedthat fibers 301 and 303 are depicted as fiber centerlines. Fibers 301and 303 are oriented in a biaxial fiber configuration. Fibers 301overlap fibers 303. In one embodiment, fibers 301 are woven about fibers303. In another embodiment, fibers 301 are woven about fibers 303 andfibers 303 are woven about fibers 301. In yet another embodiment, afirst ply comprises fibers 301 and a second ply comprises fibers 303,such that the second ply is laid-up over the first ply. Alternatively,the first ply comprises one or more of fibers 301 and fibers 303, whilethe second ply comprises fibers 301 and fibers 303 not present in thefirst ply. Moreover, the scope of the present application contemplatestwo or more of fibers 301 to be parts of a single fiber or two or moreof fibers 303 to be parts of a single fiber.

FIG. 4 depicts an alternative, illustrative embodiment of the portion oftube 103 indicated in FIG. 1. In the illustrated embodiment, tube 103exhibits a triaxial fiber configuration, comprising a plurality offibers 401 (only one labeled for clarity) extending in a third directionin addition to fibers 301 and fibers 303. Note that fibers 301, fibers303, and fibers 401 are depicted as fiber centerlines. Fibers 401overlap fibers 301 and fibers 303. In one embodiment, fibers 301 arewoven about fibers 303 and fibers 401. In another embodiment, fibers 301and fibers 303 are woven about fibers 401. In one embodiment, fibers 301are woven about fibers 303 and fibers 401, while fibers 303 are wovenabout fibers 301 and fibers 401.

Alternatively, in another embodiment, a first ply comprises fibers 301,a second ply comprises fibers 401, and a third ply comprises fibers 303,such that the second ply is disposed between the first ply and the thirdply. It should be noted, however, that the scope of the presentapplication encompasses any suitable arrangement of first, second, andthird plies. Moreover, the scope of the present application encompassesthe first, second, and third plies comprising any suitable combinationof fibers 301, fibers 303, and fibers 401. Furthermore, as in theembodiment of FIG. 3, the scope of the present application contemplatestwo or more of fibers 301 to be parts of a single fiber or two or moreof fibers 303 to be parts of a single fiber.

FIG. 5 depicts one particular illustrative configuration of the portionof tube 103 indicated in FIG. 1. In this embodiment, a plurality offibers 501 (only one labeled for clarity) extending in a first directionand a plurality of fibers 503 (only one labeled for clarity) extendingin a second direction are woven about one another such that only smallgaps (e.g., a gap 505) exist between adjacent fibers of fibers 501 andbetween adjacent fibers of fibers 503. Once tube 103 is cured (i.e., thepolymeric matrix has either hardened or crosslinked), the polymericmatrix substantially fills these gaps. Accordingly, fluids are inhibitedfrom passing through the gaps.

In an alternative embodiment, shown in FIG. 6, fibers may be spacedapart so that the polymeric matrix does not fill gaps between thefibers. In the illustrated embodiment, tube 103 comprises a plurality offibers 601 (only one labeled for clarity) extending in a first directionand a plurality of fibers 603 (only one labeled for clarity) extendingin a second direction, such that gaps (e.g., a gap 605) larger than thegaps of FIG. 5 exist between adjacent fibers of fibers 601 and betweenadjacent fibers of fibers 603. Even after tube 103 is cured, thepolymeric matrix does not completely fill the gaps. Accordingly, fluidsmay pass through the gaps.

It should be noted that certain fibers of tube 103 may differ in size ormaterial than other fibers of tube 103. Moreover, certain fibers may bewoven about only certain other fibers or may be woven about groups oftwo or more fibers. For example, in the embodiment of FIG. 7, theportion of tube 103 indicated in FIG. 1 comprises a plurality of fibers701 (only one labeled for clarity) extending in a first direction, aplurality of fibers 703 (only one labeled for clarity) extending in thefirst direction, and a plurality of fibers 705 (only one labeled forclarity) extending in a second direction. Note that fibers 703 aresmaller than fibers 701 or fibers 705. In one implementation, fibers 703comprise a different material than the material of fibers 701 and fibers705. It should be noted that the scope of the present applicationencompasses a combination of any number of fiber materials in tube 103.It should also be noted that, in some embodiments, not all of the fibersof tube 103 are individually woven about one another.

It should be noted that the embodiment of FIG. 6 may also be modified tohave the configuration of FIG. 7, in that larger gaps exist betweenadjacent fibers. It should also be noted that one or more of tubes 103may comprise woven material, such as illustrated in FIGS. 5-8B, in theform of woven broadgoods, braided sleeves, flat braids, or braidedbroadgoods. Moreover, any of the embodiments of FIGS. 5-8B may exhibit atriaxial configuration.

FIGS. 8A and 8B depict one particular illustrative configuration of theportion of tube 103 indicated in FIG. 1. In this embodiment, a pluralityof fibers 801 (only one labeled for clarity) extending in a firstdirection and a second direction are woven with one or more removablebands 803, about one another. Removable bands 803 are configured to beremoved in a post cure operation, thus producing gaps 805. For example,removable bands 803 may include a soluble material such that a flushingexposure to water would dissolve and remove bands 803, thereby producinggaps 805 (as shown in FIG. 8B). Removable bands 803 may be introduced ina variety of configurations and quantities, thereby producing selectedweave pattern. The configurations of removable bands 803 with pluralityof fibers 801 can be selectively chosen to produce gaps 805 andconfigured for a selected flow rate between and among cells 105 of core101.

As shown in FIG. 2, adjacent sides of tubes 103 are adhesively bonded,or otherwise attached, to one another to form core 101. FIGS. 8C and 9depict enlarged views of a portion, indicated in FIG. 2, of core 101. Inthe embodiment of FIG. 8C, adhesive bonds between tubes 103 are formedby polymeric matrices of adjacent tubes 103. In other words, thepolymeric matrix of one tube 103 bonds directly to the polymeric matrixof an adjacent tube 103. Fibers in one tube 103 are crosslinked withfibers of adjacent tube 103, which is further described in regard toFIG. 24. Alternatively, as depicted in FIG. 9, adhesive bonds betweentubes 103 are provided by an adhesive layer 901 disposed between tubes103.

Returning to FIG. 2, tubes 103 exhibit any desired cross-sectionalheight H. For example, core 101 may include tubes 103 having a height Hof about six millimeters or may include tubes 103 that have the height Hof about 50 millimeters. The scope of the present application, however,is not limited by these exemplary heights H. Rather, core 101 maycomprise tubes 103 having any desired size, e.g., height H. Moreover,core 101 may comprise different sized tubes 103. In other words, core101 may comprise one or more tubes 103 having sizes that are differentfrom one or more other tubes 103. For example, core 101 may comprisetubes 103 having different heights H.

Tubes 103 of the embodiment illustrated in FIGS. 1 and 2 exhibithexagonal cross-sectional shapes. The scope of the present application,however, is not so limited. Rather, a core of the present applicationmay comprise tubes having any shape suitable for the implementation ofthe core. For example, as shown in FIG. 10, a core 1001 comprises aplurality of rectangular tubes 1003. Note that only two tubes 1003 arelabeled in FIG. 10 for clarity. As in the previous embodiment, adjacenttubes 1003 are adhesively bonded, or otherwise attached, to one another.Other aspects of tubes 1003 generally correspond to the aspects of tubes103 discussed above and shown in FIGS. 1-9.

The core of the present application, such as core 101 (shown in FIGS. 1and 2) and core 1001 (shown in FIG. 10), may be produced using anysuitable method. It should be noted that, while the particularmanufacturing embodiments discussed below and illustrated in thedrawings are directed to the manufacture of core 101, the embodimentsapply equally to the manufacture of core 1001 or any other coreencompassed within the scope of the present application.

In one embodiment, shown in FIG. 11, tube 103 (shown in FIGS. 1 and 2)is made by braiding a sleeve 1101 of fibers 1103 (only one labeled forclarity) using a braiding machine 1105. Sleeve 1101 may comprise, forexample, a biaxial arrangement of fibers 1103 or a triaxial arrangementof fibers 1103, as discussed above. Fibers 1103 may comprise dry fibersor resin-coated fibers, such as fibers coated with a thermoplasticresin. As shown in FIG. 12, sleeve 1101 is place over a mandrel 1201after sleeve has been braided. Note that, in the illustrated embodiment,mandrel 1201 exhibits a size and shape corresponding to cell 105 (seeFIG. 1 or 2). Mandrel 1201 and sleeve 1101 are subsequently assembledwith other mandrels and sleeves, as will be discussed in greater detailbelow, to form core 101 (shown in FIG. 1).

It should be noted that, as shown in FIG. 13, sleeve 1101 may be braideddirectly onto mandrel 1201. In such an embodiment, fibers 1103 aresecured to mandrel 1201, if only frictionally, prior to braiding sleeve1101. Braiding machine 1105 may be advanced along mandrel 1201, asindicated by an arrow 1301, as sleeve 1101 is braided. Mandrel 1201 maybe advanced with respect to braiding machine 1105, as indicated by anarrow 1303, instead of or in addition to braiding machine 1105 beingadvanced along mandrel 1201.

In another embodiment, shown in FIG. 14, tube 103 (shown in FIGS. 1 and2) is made using a filament winding process. A continuous,resin-impregnated fiber 1401, extending from a filament winding machine1403, is wound about a mandrel 1405. The resin can be either athermosetting or thermoplastic resin and becomes the polymeric matrix oftube 103 upon curing tube 103. The material placement process may beconducted in a variety of processes; however, it is preferred that themandrel 1405 moves axially while a spool of fiber 1401 rotates aroundthe mandrel 1405, as indicated by an arrow 1407. Alternatively, a spoolor a plurality of spools of material could rotate around the mandrel.Relative motion of the material dispensing mechanism to the mandrel isinferred. As fiber 1401 is wound onto mandrel 1405 by filament windingmachine 1403, a helical shaped pattern is formed. One or more plies 1409of fiber 1401, in desired orientations with respect to mandrel 1405, arewound onto mandrel 1405 to form tube 103. The angle of which fiber 1401is wound about mandrel 1405 may vary along the length of the mandrel1405 in order to customize the strength of the core. For example, theangle of the fiber 1401 may be dynamically changed during the materialplacement process in order to customize a compressive strength of thecore. Note that, in the illustrated embodiment, mandrel 1405 exhibits asize and shape corresponding to cell 105 (see FIG. 1 or 2). It should befurther noted, however, that the present application is not limited tothe particular illustrated configurations of filament winding machine1403 or mandrel 1405. Mandrel 1405 and the one or more plies 1409 thathave been filament wound onto mandrel 1405 are subsequently assembledwith other mandrels and plies, as will be discussed in greater detailbelow, to form core 101 (shown in FIG. 1). It should further beappreciated that upon cutting of plies 1409 and the mandrel 1405, thematerial may have a tendency to un-wind. A band of material, potentiallyadhesive or fiberous, may be used to keep fiber 1401 from unravelingupon cutting of the plies 1409 and the mandrel 1405. An adhesivematerial with unidirectional fibers could be used to band the fiber 1401on mandrel 1405 and remain compatible with the base material.

In yet another embodiment, shown in FIG. 15, tube 103 (shown in FIGS. 1and 2) is made using a fiber placement process. A continuous,resin-impregnated tow 1501 (only one labeled for clarity) ofapproximately 1000 fibers is applied to a mandrel 1503 by a fiberplacement machine 1505. It should be appreciated that tow 1501 may alsobe portions of a full tow; for example, tow 1501 may be a half tow of500 fibers. In lieu of a tow 1501, a tape of fibers, cut to a prescribedwidth, may be used. A pre-cut tape of fibers may be referred to as a“slit-tape.” A slit-tape allows the user to more closely control thewidth dimension, as compared to a tow of fibers. Exemplary prescribedwidths of slit-tape include ⅛″ and ¼″, to name a few. The resin can beeither a thermosetting or thermoplastic resin and becomes the polymericmatrix of tube 103 upon curing tube 103. During the fiber placementprocess, mandrel 1503 moves axially while tow 1501 rotates around themandrel 1503, as indicated by an arrow 1507. As tow 1501 is applied tomandrel 1503 by fiber placement machine 1505, a helical shaped patternis formed. One or more plies 1509 of tow 1501, in desired orientationswith respect to mandrel 1503, are wound onto mandrel 1503 to form tube103. It should be appreciated that more than one tow 1501 of differentmaterials may be used. Note that, in the illustrated embodiment, mandrel1503 exhibits a size and shape corresponding to cell 105 (see FIG. 1 or2). It should be further noted, however, that the present application isnot limited to the particular illustrated configurations of fiberplacement machine 1505 or mandrel 1503. Mandrel 1503 and the one or moreplies 1509 that have been fiber placed onto mandrel 1503 aresubsequently assembled with other mandrels and plies, as will bediscussed in greater detail below, to form core 101 (shown in FIG. 1).

It is important to note that adjacent tubes 103, as best shown in FIG.1, are located so that fibers in a first tube 103 crosslink with fibersin an adjacent tube 103 where adjacent tubes 103 contact each other, asshown in FIG. 8C. Referring to FIG. 24 as an illustrative embodiment,fibers 2401 are represented as dashed lines in order to clarify thatfibers 2401 are from a tube 103 adjacent to another fibers 2403 ofanother tube 103, as shown in FIG. 1. It should be appreciated thatfibers 2401 and 2403 may be actual individual fibers, or centerlines fora plurality of fibers, such as fibers in tow 1501. In the example shownin FIG. 24, tubes 103 are created by winding fibers about a mandrel atan angle (such as mandrels 1405 and 1503) as shown in FIGS. 14 and 15.Fibers 2401 and 2403 are each wound about a different mandrel, but in asimilar orientation. However, when mandrels are placed together in amold, as shown in FIG. 18, fibers 2401 and 2403 are oriented to eachother in a crosslinking pattern. For example, when fibers 2401 and 2403are each wound about a mandrel at a same direction and a same 45 degreeangle, then fibers 2401 and 2403, of adjacent tubes 103, actually have a90 degree crosslinking orientation to each other. It should beappreciated that multiple mandrels having similarly oriented woundfibers are assembled adjacently, without changing the orientation of themandrels, so as to produce crosslinking of fibers in adjacent tubes 103.After curing, crosslinked fibers 2401 and 2403 provide strength to core101. It should be appreciated that fibers 2401 and 2403 of adjacenttubes 103 can be wound about a mandrel in a variety of orientations; forexample, fibers 2401 and 2403 may be wound about a mandrel at 30 degreeorientations such that fibers 2401 and 2403 are crosslinked at 120degree orientations to each other. It should also be appreciated thatfibers 2401 and 2403 may be braided, instead of being wound, ontomandrels in a variety of patterns; nevertheless, fibers 2401 and 2403 ofadjacent tubes 103 become further crosslinked during processing. Anexemplary method of processing multiple adjacent tubes 103 to form core101 is described in relation to FIGS. 17-20.

Alternatively, tube 103 (shown in FIGS. 1 and 2) may be made usingmanual, hand-layup methods. For example, as shown in FIG. 16, one ormore plies 1601 having desired fiber orientations are applied onto amandrel 1603 to form tube 103. The one or more plies 1601 may comprisewoven dry fibers, unwoven dry fibers, resin-impregnated woven fibers, orresin-impregnated unwoven fibers. Note that, in the illustratedembodiment, mandrel 1603 exhibits a size and shape corresponding to cell105 (see FIG. 1 or 2). It should be further noted, however, that thepresent application is not limited to the particular illustratedconfigurations of the one or more plies 1601 or mandrel 1603. Mandrel1603 and the one or more plies 1601 that have been applied onto mandrel1603 are subsequently assembled with other mandrels and plies, as willbe discussed in greater detail below, to form core 101 (shown in FIG.1).

As shown in FIG. 17, a plurality of mandrels 1701 (corresponding tomandrels 1201, 1405, 1503, 1603, or the like) and tubes 103 areassembled together to form the basis for core 101 (shown in FIG. 1).Note that the plurality of mandrels 1701 and tubes 103 may include anysuitable number of mandrels 1701 and tubes 103 in any suitableconfiguration to form core 101. In one embodiment, shown in FIG. 18, theplurality of mandrels 1701 and tubes 103 are assembled together in amold 1801. Note that mold 1801 is not limited to the configurationdepicted in FIG. 18 but may take on any suitable configuration. An innersurface 1803 of mold 1801 has the form of an exterior surface 107 (seeFIG. 1) of core 101.

In one embodiment, tubes 103 comprise a thermosetting polymeric matrixthat is cured prior to assembling mandrels 1701 and tubes 103 into mold1801. In such an embodiment, adhesive layer 901 (shown in FIG. 9) isapplied between adjacent tubes 103 prior to assembling mandrels 1701 andtubes 103 into mold 1801. In another embodiment, tubes 103 comprise athermoplastic polymeric matrix or comprise a thermosetting polymericmatrix that is not cured prior to assembling mandrels 1701 and tubes 103into mold 1801. In such an embodiment, adhesive layer 901 may be appliedbetween adjacent tubes 103 prior to assembling mandrels 1701 and tubes103 into mold 1801, but is not required.

If fibers pre-impregnated with polymeric resin are used in tubes 103,heat and, in some embodiments, pressure is applied to tubes 103 aftermandrels 1701 and tubes 103 have been assembled into mold 1801. If tubes103 are not cured prior to assembly into mold 1801, the applied heatcures tubes 103. If adhesive layers 901 are used to adhesively bondadjacent tubes 103, the applied heat melts and cures adhesive layers901.

If dry fibers are used in tubes 103, in one embodiment, a thermoplasticor thermosetting polymeric resin is introduced about the dry fibers viaone or more ports 1805, 1807. The polymeric resin becomes the polymericmatrix of tubes 103. Processes such as resin transfer molding,vacuum-assisted resin transfer molding, or the like can be used toaccomplish the introduction of the polymeric resin about the dry fibers.Heat and, in some embodiments, pressure is applied to tubes 103 to curethe polymeric resin.

After the adjacent tubes 103 are adhesively bonded to one another toform core 101, mandrels 1701 are removed from tubes 103. In oneembodiment, mandrels 1701 are merely withdrawn from tubes 103. In otherembodiments, however, mandrels 1701 are dissolved, for example, by heator a solvent. In one embodiment, mandrels 1701 are water soluble and,thus, water is used to dissolve mandrels 1701. In the embodiment whereinthe mandrel is dissolvable, the mandrel may remain the core to aid instabilizing the core during machining of the core. The mandrel may alsoremain inside the core after machining and during the processing andcuring of the core to the skins in order to stabilize the core duringthe processing and curing. Next, the mandrel could be dissolved withwater, or removed through a similar means. It should be appreciated thatthe mandrels can also be comprised of several layers, including anoutside soluble material that remains with the core, and an inside metalmaterial that is removed after the core is processed.

FIGS. 19 and 20 represent another illustrative embodiment a mandrel 1901used to create core 101. An expandable mandrel 1901 may be used suchthat tubes 103 are formed on expandable mandrels 1901 for formation ofcore 101. Expandable mandrel 1901 is preferably constructed of amaterial that expands in volume when subjected to heat, or any othercatalyst that would tripper volumetric expansion. Expandable mandrels1901, with tubes 103, are then stacked and arranged in a selectedpattern while in their pre-expanded state, as shown in FIG. 19.Expandable mandrels 1901 are preferably confined in a mold 1801 suchthat volumetric expansion of expandable mandrels 1901 forces tubes 103to formed to a specified shape and pattern. The pattern shown in FIGS.19 and 20 is merely exemplary of a variety of shapes and patterns towhich expandable mandrels 1901 can be arranged. For example, mandrels1901 can be stacked directly adjacent, above, and below so as to formtubes 103 into a square shape. One exemplary advantage of expandablemandrels 1901 is that a variety of core 101 shapes can be manufacturedfrom a single sized mandrel. In addition, it is simpler to wind fibersonto a round mandrel versus a multi-faceted mandrel.

The scope of the present application encompasses a composite sandwichstructure comprising a core of the present application. For example,FIGS. 21 and 22 illustrate a side, elevational view and a top, planview, respectively, of a composite sandwich structure 2101 according tothe present application. As shown in FIG. 23, which is a cross-sectionalview of a portion of composite sandwich structure 2101, compositesandwich structure 2101 comprises a core 2301 disposed between an upperskin 2303 and a lower skin 2305. Upper skin 2303 is adhesively bonded toan upper face 2307 of core 2301 by a first adhesive layer 2309. Lowerskin 2305 is adhesively bonded to a lower face 2311 by a second adhesivelayer 2313. It should be noted that, in various embodiments, one ofupper skin 2303 and lower skin 2305 may be omitted.

In one embodiment, adhesive layers 2309, 2313 extend substantially onlybetween core 2301 and skins 2303, 2305, respectively. In other words,adhesive layers 2309, 2313 are omitted over open cells 2315 of core2301. This configuration is accomplished, in one embodiment, byconcentrating adhesive on the edge surfaces of the core through areticulation process.

The particular embodiments disclosed above are illustrative only, as theapplication may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Furthermore, no limitations are intended to thedetails of construction or design herein shown, other than as describedin the claims below. It is therefore evident that the particularembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of theapplication. Accordingly, the protection sought herein is as set forthin the claims below. It is apparent that an application with significantadvantages has been described and illustrated. Although the presentapplication is shown in a limited number of forms, it is not limited tojust these forms, but is amenable to various changes and modificationswithout departing from the spirit thereof.

What is claimed is:
 1. A method of making a composite core sandwichstructure, comprising: providing a plurality of tubes, each of theplurality of tubes including a plurality of fibers disposed in apolymeric matrix; using a mandrel to provide an internal form for theplurality of fibers of each of the plurality of tubes; placing theplurality of fibers of each tube in contact with the plurality of fibersof adjacent tubes, such that the plurality of fibers of adjacent tubeshave a crosslinked orientation; bonding a first face sheet to a firstend portion of the plurality of tubes; and bonding a second face sheetto a second end portion of the plurality of tubes.
 2. The method,according to claim 1, wherein the mandrel is a round expandable mandrelsuch that the round expandable mandrel expands when heated while beingconfined in an arrangement so as to form each tube in a hexagonal shape.3. The method, according to claim 1, wherein the providing the pluralitytubes is accomplished by: providing the plurality of fibers as a braidedsleeve; curing a polymeric resin about the plurality of fibers of thebraided sleeve to form the polymeric matrix.
 4. The method, according toclaim 3, further comprising: infusing the polymeric resin into thebraided sleeve before the curing the polymeric resin.
 5. The method,according to claim 1, wherein the providing the plurality of tubes isaccomplished at least in part by a filament winding process.
 6. Themethod, according to claim 1, wherein the providing the plurality oftubes is accomplished at least in part by a fiber placement process.